1. Field of the Invention
The invention relates to a composition having a bismaleimide oligomer, and more particularly to a composition having high-pure bismaleimide oligomer without purification.
2. Description of the Related Art
Bismaleimide is widely used in fabrication of circuit boards, as an adhesive, copper clad laminates, or resin coated coppers, due to a high glass transition temperature, thermostability, mechanical strength, toughness, and superior physics and electrical characteristics. Bismaleimide polymer obtained by hardening, however, has a high density network structure and exhibits increased brittleness, high moisture absorbability, bad adhesion, and low solubility, resulting in limited applicability.
To overcome the aforementioned drawbacks of the maleimide resin composition, various proposals have been made.
U.S. Pat. No. 5,041,519, the content thereof is incorporated herein by reference, discloses an improved epoxy resin composition which exhibits high glass transition temperature and good toughness. The epoxy resin composition disclosed in the '519 patent comprises a specific epoxy resin, a bismaleimide resin, and barbituric acid. While the epoxy composition of the '519 patent provided several improved physical and electrical properties, it was designed to be used as a substrate in IC packaging, and cannot be used, and was not expected to be used, as an adhesive.
U.S. Pat. No. 5,112,924 discloses a thermosetting composition comprising a multifunctional maleimide and a terminally unsaturated polyamide, polyimide, or polyamideimide oligomer which is soluble in the thermosetting composition. However, with this method, the glass transition temperature and toughness are somewhat reduced, and cost and reaction complexity are substantially increased, thereby limiting application range.
U.S. Pat. No. 5,326,794 discloses a process for manufacturing a high glass transition temperature printed circuit board comprising blending a modified bismaleimide resin into a modified epoxy resin. The material is manufactured by blending a bismaleimide resin reacted with barbituric acid and its derivative thereof and an epoxy resin with an oxazolidone ring resulting from the reaction of a polyisocyanate and an epoxy resin modified with a secondary diamine and followed by curing. The resultant product has a high glass transition temperature, good adhesion, flame retardancy, and low bromine content. However, the bismaleimide and epoxy resin must be modified before blending, resulting in an increase in cost and time. Further, the obtained, so-called, ‘improved’, product characteristics are not very obvious.
Commercially available bismaleimide thermoset compositions are noted for their high modulus, and excellent resistance to thermal degradation. However, the thermoset compositions are also well known for brittleness. The utility of the bismaleimide class of thermosets would be vastly improved, if brittle formulations could be lessened while retaining desirable thermal and elastic properties.